The 7th Indonesia Japan Joint Scientific Symposium (IJJSS 2016) Chiba, 20-24 November 2016 Topic: Earth and Planetary Science Sedimen Deposit of Floodplain Formation Resulting From Lateral Accretion Surfaces on Tropical Area: Study Case at Kampar River, Indonesia Yuniarti Yuskar a, *, Tiggi Choanji a a Geological Engineering, Universitas Islam Riau, Jl. Kaharuddin Nasution No 113 Pekanbaru, 28284, Indonesia Abstract Kampar rivers has a length of 413 km with average depth of 7.7 m and width of 143 m. Sixty percent of this rivers are meandering fluvial system which transport and deposit a mixture of suspended and bed-load (mixed load) along low energy. River channel that moving sideways by erosion is undergoing lateral migration and the top of the point bar becomes the edge of the floodplain and the fining-upward succession of the point bar will be capped by overbank deposits of Kampar River. Along the Kampar Rivers, there are more than 60% of floodplain sediments and almost all of the floodplain formed by bend migration on the suspended-load channels of Kampar watershed. This formation consist of succession of fine to medium sand and silt/mud, with root traces, that form as drapes on the prograding bank. These beds dip mostly channel wards and quickly wedge out as they grade up and onto the floodplain. The depositional model is presented showing how lateral accretion can make a significant contribution to the preservation of fine-grained within channel deposits in contemporary floodplains. The examples presented here demonstrate that analogues to ancient point-bar deposits containing alternating sandstone and shale sequences are common in the low-energy fluvial environments of Riau rivers especially Kampar rivers. Keywords Kampar Rivers, lateral accretion, floodplain, meandering, depositional model. 1. Introduction Meanders develop by erosion of the bank closest to the thalweg, accompanied by deposition on the opposite side of the channel where the flow is sluggish and the bed-load can no longer be carried and river is considered to be meandering if there is accumulation of sediment on the inside of bends. Meandering rivers transport and deposit a mixture of suspended and bed-load (mixed load) a long low energy. The bed-load is carried by flow in the channel, with the coarsest material carried in the deepest parts of the channel. Finer bed-load is also carried in shallower parts of the flow and it is deposited along the inner bend of a meander loop where friction reduce the flow velocity (Nichols, 2009). Type of sediment is formed by meandering pattern are channel deposit, point bar, natural leeve, floodplain, oxbow lake, and crevasse splay. * Corresponding Author, Yuniarti Yuskar. Tel.: +62-822-6790-2974. E-mail address: yuniarti_yuskar@eng.uir.ac.id